Expression of c-KIT and its ligand, stem cell factor, in normal and subfertile human testicular tissue

The c‐KIT proto‐oncogene encodes for a transmembrane receptor and is associated with maturation of several cell types, including germ cells. The ligand of the receptor has been identified as stem cell factor (SCF). Loss or alteration of the expression of either of these factors leads to anemia, albinism, and/or sterility in mice. We examined the expression of c‐KIT and SCF by immunohistochemistry in specimens from normal and infertile human testis. All specimens were obtained in the evaluation of male subfertility. We were able to demonstrate staining for c‐KIT in Leydig cells in all specimens. Normal testis stained for c‐KIT in the cytoplasm of early spermatogenic cells, as well as the acrosomal granules of the round spermatids and the acrosome of testicular spermatozoa. However, staining in testis demonstrating maturation arrest failed to demonstrate acrosomal staining, and Sertoli‐only specimens demonstrated staining for c‐KIT in Leydig cells only. The results for SCF demonstrated an overall uniform staining of Leydig cells in all specimens. The intensity of staining of Sertoli cells increased from normal to maturation arrest to Sertoli‐only specimens. Germ cell staining was consistently negative. We hypothesize that these staining patterns for SCF are due to either lack of staining of the receptor‐ligand complex or overexpression of the kit ligand in tissue that does not express the kit receptor. It appears that the c‐kit receptor is expressed in the acrosome of developing germ cells, as well as in Leydig cells and early spermatogenic cells, suggesting a role in the acrosome reaction, as well as germ cell maturation and differentiation.